1. Field of the Invention
The invention pertains to pharmacologically active 3,6-disubstituted pyran compounds and similar compounds having additional substitution on the pyran ring. The compounds show high activity at monoamine transporters, and thus can be used to alter reuptake of monoamines in treatment of numerous diseases in mammalian species for which alteration of the monoamine transport system is indicated.
2. Background Art
The monoamine transporters terminate the action of released biogenic amines such as dopamine (DA), norepinephrine (NE) and serotonin (5-HT) in the central nervous system (CNS) and are known as dopamine transporter (DAT), norepinephrine transporter (NET) and serotonin transporter (SERT), respectively.1 These transporters play a vital role in maintaining the extracellular concentration of biogenic amine neurotransmitters.2 Drugs binding to the DAT are typically regarded as stimulants. Cocaine- and amphetamine-related compounds are known to produce their action by binding to both DAT and SERT with cocaine acting as a blocker and amphetamine as a substrate.3-7 On the other hand, drugs binding to the SERT and NET are known to produce, among other effects, potent antidepressant activity.8-10 
Major depression disorder is a significant health problem, and behind cardiovascular disease, depression is considered as the second most debilitating disease in the world. Unipolar depression is ranked number 1 before all other somatic and psychiatric illness. It is believed that more than 20% of individuals suffer from a depressive episode at least once in their lifetime. Depression is potentially fatal since many people suffering from depression contemplate suicide and other life threatening acts.
Selective monoamine uptake inhibitors have been implicated in the treatment of depression.11 In these classes specifically, serotonin and norepinephrine transporter blockers have been used in therapy for depression.12,13 Antidepressants are thought to elicit their therapeutic effects by increasing synaptic concentrations of serotonin and norepinephrine in the synapse.14 Earlier developed tricyclic antidepressants acted by enhancing both serotonin and norepinephrine transmissions.15 However, due to their non-specific interactions with the other CNS receptors, they exhibited toxic side effects which have limited their clinical use.16,17 Development of selective serotonin reuptake inhibitors (SSRI) alleviated many side effects exhibited by traditional trycyclic antidepressants and thus have proven to be more effective.18-20 However, the delayed onset action of SSRI sometime proved to have fatal consequences for patients afflicted with manic depression and in need of immediate help. SSRIs also have been implicated in number of other side effects which include insomnia, sexual dysfunction and nausea, etc. More recently, SSRIs have been implicated in suicide risk in adolescent population who were medicated with these drugs, raising some serious questions on the safety of SSRI. Lately, serotonin and norepinephrine dual uptake inhibitors have proven to be more efficacious in that regard. Fast onset of action associated with serotonin norepinephrine reuptake inhibitors (SNRI) was found to be more desirable as there is a pressing need for more faster acting antidepressant agents with reduced undesirable side effects.